1. Field of the Invention
The present invention relates to a temperature detection circuit, in particular, a temperature detection circuit which outputs a voltage or a current proportional to a chip temperature when a power consumption in a chip such as a power IC is on a high level and the chip temperature is required to be detected, and a semiconductor device mounting this temperature detection circuit.
2. Description of Related Art
In recent years, in general, the integration of LSI has been advanced, and many of circuits are being mounted within one chip. Power consumption is increased in proportion to a scale of the circuit. Alternatively, even when many of circuits are not mounted, a circuit such as a power IC consumes inherently high power. In such a case, the chip temperature rises, and in the worst case, the chip is likely broken down. To avoid this, it is desirable to detect the chip temperature of the semiconductor device and control the system of the semiconductor device, thereby protecting the chip as a result. For example, a temperature sensor is mounted in the semiconductor device. In this case, as the temperature sensor, a circuit (temperature detection circuit) for outputting a voltage or current proportional to the temperature of the semiconductor chip is considered to be mounted.
FIG. 17 shows a graphic chart representing a chip temperature in the axis of abscissas, and an output voltage in the axis of ordinate. The figure shows that the chip temperature and the output voltage are in a directly proportional relationship. As shown in FIG. 17, when the chip temperature is 25° C., the output voltage is 0 V, and when it is 75° C., the output voltage is V1, and when it is 125° C., the output voltage is V2.
Japanese Patent Laid-Open publication No. 11-258065 discloses a temperature detection circuit realizing the characteristics of FIG. 17. FIG. 18 is a circuit diagram showing the temperature detection circuit disclosed in the Publication. As shown in FIG. 18, a temperature detection circuit 210 comprises a band gap reference circuit (hereinafter, referred to as BGR circuit) 213, first and second operational amplifiers A31 and A32, first to fourth resistors R21 to R24, first and second diodes D11 and D12, and a current source Ill.
The operational amplifier A32 is inputted with the output voltage of a BGR circuit 113 in a non-inverting input terminal (forward rotation input terminal), and has a resistor R21 connected between the inverting input terminal and a GND, and further, has a resistor R22 connected between the inverting input terminal and the output terminal.
Further, the first diode D11 has its anode connected to the output terminal of the second operational amplifier A32, and has its cathode connected to the anode of the second diode D12. The current source I11 has one end connected to the cathode of the second diode D12, and has the other end connected with the GND. The operational amplifier A31 has the non-inverting input terminal connected to the cathode of the second diode D12, and has a resistor R23 connected between the inverting input terminal and the GND, and further, has a resistor R24 connected between the inverting input terminal and an output terminal VOUT. The output terminal of this operational amplifier A31 is the final output terminal OUT.
When the temperature detection circuit 210 takes the voltage of the BGR circuit 213 as a VBGR, an output voltage VREF of the operational amplifier A32 can be represented by the following formula (1).
                    [Formula  1]                                                                      V          REF                =                              V            BGR                    ⁡                      (                          1              +                                                R                  22                                                  R                  21                                                      )                                              (        1        )            
Since the output voltage VREF is applied to anode sides of the two diodes D11 and D12 connected in series, and is biased by the current source I11, when the current flowing into the current source I11 is taken as a current I11, the cathode voltage VD12k of the diode D12 can be represented in the following formula (2).
                    [Formula  2]                                                                      V                      D            ⁢                                                  ⁢            12            ⁢            K                          =                                            V              BGR                        ⁡                          (                              1                +                                                      R                    22                                                        R                    21                                                              )                                -                      2            ⁢                                                  ⁢                          kT              q                        ⁢            ln            ⁢                                                  ⁢                                          I                11                                            I                S                                                                        (        2        )            Here is shown a reversed saturation current for the diode, where k: Boltzman's constant, T: the absolute temperature, q: charge of electron, and IS: diode.
Now, it is generally known that the temperature characteristic corresponding to one piece of the diode has a temperature characteristic of an approximately −2 mv/° C. Further, when the BGR circuit 113 is correctly designed, the temperature characteristic, as compared with the temperature characteristic of the diode, can be reduced approximately to the point of ignoring the same. Consequently, to check the temperature characteristic of the formula (2), assuming that the voltage (KT/q)In(I11/IS) of the diode is −2 mv/° C., the formula (2) is differentiated by a temperature T, and the following formula (3) is established.
                    [Formula  3]                                                                                  ⅆ                          ⅆ              T                                ⁢                      V                          D              ⁢                                                          ⁢              12              ⁢              K                                      ≅                              +            4                    ⁢                                          ⁢          mV          ⁢                      /                    ⁢                      °C            .                                              (        3        )            As a result of amplifying this voltage VD12K by a closed loop gain decided by the operational amplifier A31, the resistor R23, and the resistor R24, the final output voltage Vout becomes as follows.
                    [Formula  4]                                                                                                                V                out                            =                                                V                                      D                    ⁢                                                                                  ⁢                    12                    ⁢                    K                                                  ⁡                                  (                                      1                    +                                                                  R                        24                                                                    R                        23                                                                              )                                                                                                        =                                                (                                      1                    +                                                                  R                        24                                                                    R                        23                                                                              )                                ⁢                                  {                                                                                    V                        BGR                                            ⁡                                              (                                                  1                          +                                                                                    R                              22                                                                                      R                              21                                                                                                      )                                                              -                                          2                      ⁢                                                                                          ⁢                                              kT                        q                                            ⁢                      ln                      ⁢                                                                                          ⁢                                                                        I                          11                                                                          I                          S                                                                                                      }                                                                                        (        4        )            
Further, the temperature characteristic of this voltage VD12K has the characteristic shown in the formula (3), and thus, the output voltage Vout becomes as follows.
                    [Formula  5]                                                                                  ⅆ                          ⅆ              T                                ⁢                      V            out                          ≅                              +            4                    ⁢                                          ⁢                      (                          1              +                                                R                  14                                                  R                  13                                                      )                    ⁢                                          ⁢          mV          ⁢                      /                    ⁢                      °C            .                                              (        5        )            That is, the temperature detection circuit having a desired positive inclination decided by the resistors R23 and R24 can be realized.
However, a temperature detection circuit 210 disclosed in the publication has a problem that the output voltage is unable to obtain an accuracy of the voltage output in the vicinity of 0 V. This is because, when the current source I11 is configured by the transistor, the input voltage is not allowed to operate as a constant current source in the vicinity of the input voltage 0 V. Further, since the temperature characteristic corresponding to two pieces of the diode is obtained by being amplified by the operational amplifier A31, if the temperature characteristic of the diode has an inherent error component, there arises a problem also that the error component is amplified by an amplification factor decided by the operational amplifier A31 and the resistors R23 and R24.